Method of manufacturing tubes of compound material

ABSTRACT

In manufacturing tubes of compound material by hydrostatic extrusion through a die, the front end of the billet is formed with a taper to fit the conical inlet of the die. The mating line between the lower ends of the core and the casing is within the die, so that when extrusion starts only the casing is in contact with the die and only the core with the mandrel. This prevents any possible entry of pressure fluid between the core and the casing.

United States Patent [191 Nilsson Apr. 30, 1974 METHOD OF MANUFACTURING TUBES OF COMPOUND MATERIAL [75] Inventor: Jan Nilsson, Robertsfors, Sweden [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden [22] Filed: Mar. 1, 1972 [21] Appl. No.: 230,895

[30] Foreign Application Priority Data Mar. 15, 1971 Sweden 3273/71 [52] US. Cl 29/474.3, 72/60, 72/264 [51] Int. Cl. B2lc 23/22 [58] Field of Search 72/60, 258, 264; 29/4743 [56] I References Cited UNITED STATES PATENTS 3,580,019 5/1971 Beresnev et al 72/47 3,654,687 4/1972 Burstrom et al. 72/60 3,631,586 l/l972 Bearpark et a1. 29/4743 3,391,563 7/1968 Donegan 72/258 3,702,556 11/1972 Larker et a1. 72/60 3,604,102 9/1971 Boccalari et al 29/4743 Primary ExaminerRichard J. Herbst [5 7] ABSTRACT In manufacturing tubes of compound material by hydrostatic extrusion through a die, the front end of the billet is formed with a taper to fit the conical inlet of the die. The mating line between the lower ends of the core and the casing is within the die, so that when extrusion starts only the casing is in contact with the die and only the core with the mandrel. This prevents any possible entry of pressure fluid between the core and the casing.

12 Claims, 2 Drawing Figures memenm 30 m,

SHEET 1 0F 2 PATENTED R 30 1974 SHEET 2 BF 2 METHOD OF MANUFACTURING TUBES OF COMPOUND MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing tubes of compound material and a billet for use with the method.

2. The Prior Art Through, for example, US. Pat. No. 3,620.059, it is known that so-called compound material can be produced by means of hydrostatic extrusion, i.e., wire or rods having a core of one material surrounded by a casing of another material, an extremely strong bond being obtained between core and easing.

It is also known, through Nilsson et al. application No. 145,184, now U.S. Pat. No. 3,751,958, that tubes can be produced by means of hydrostatic extrusion, a mandrel being applied in the orifice of the die and the material extruded through the gap between the mandrel and the die.

It is also known to produce tubing of compound material by means of hydrostatic extrusionfHowever, it has been found thatv there are serious technical and economical problems involved with this. For instance, there have been problems in preventing the pressure medium used from penetrating between the casing and the core of the billet at the front part which is in contact with the die. For obvious reasons, no special sealing members can be used here of the type known for use at the rear end of the billet. Even a very slight penetration of the pressure medium between the core and the casing can completely destroy the bond between core and casing in the finished product.

It is known for the casing to be in the shape ofa tube which is fitted or forced onto the hollow core. The latter is then bevelled at the front end in order to fit the correspondingly conical opening of the die orifice. This bevelled part is a considerable portion of the billet and in previous methods of tubular extrusion a constant ratio between the area of material in the core and in the casing of the finished product will not be obtained until this front part has been pressed out through the die. A considerable part of the material produced will therefore fall outside the production tolerances and must be scrapped. This is a serious economic drawback since scrap of combined metals usually has very low value.

The invention refers to a method in which these problems and drawbacks are completely eliminated, and to a billet for use with the method according to the invention.

SUMMARY OF THE INVENTION The characteristic feature of the invention is that a billet composed of a core and a casing is hydrostatically extruded through a die having a conical inlet and around a mandrel. In order to prevent the entry of the pressure fluid between the front ends of the core and the casing, these are tapered and are so arranged that the line of joining between them at the lower end lies within the opening of the die. The proportion of the thickness of the tapered portions is the same at each point as in the main body of the billet.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying FIGS. 1 and 2 in which FIG.

1 shows a billet inserted in the pressure chamber for extruding according to the method, and FIG. 2 shows a tool for upsetting the end of the billet facing the die.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a pressure chamber having a cylindrical mantle 1. Its base is a press plate 2. A die 3 is placed against the press plate and has an opening with the same shape and dimensions as the outer contour of the diameter of the finished product. A sealing ring 4 seals between the die and the mantle. A mandrel 5 is placed in the desired position in the opening of the die so that a gap 6 is formed between die and mandrel, this gap having a shape and width corresponding to the wall thickness of the finished product. The mandrel 5 is shown narrowing in the direction of the die, but it may have a constant diameter if preferred. In the latter case the mandrel may be attached to the billet in the axial direction and thus will follow the billet out through the die during the extrusion. Another possibility is to attach the mandrel in the axial direction with relation to the pressure chamber by means known per se, not shown.

The billet consists of a tubular core 7 and a tubular casing 8. The tubes may have free clearance in relation to each other and to the mandrel so that the core can be inserted-in the casing without difficulty and then the billet fitted easily over the mandrel upon insertion in the pressure chamber.

A sealing member 9 consisting of a ring of plastic or suitable metal with flanges folded down over the core and the casing is arranged at the rear end of the billet to p event pressure medium from penetrating between the core and the casing. Alternatively, a sealing ring may be applied between core and casing close to the rear end of the billet.

The core 7 is provided with a groove 10. The casing 8 is pressed mechanically or hydrostatically into this groove so that core and easing are fixed to each other in the axial direction. The attachment of core and casing may also be carried out in some other manner, known per se, for example by welding them to each other, a seal then being obtained at the same time.

Behind the billet is a piston 12, freely movable in the chamber, sealing members 13 and 14 being provided to seal against the mantle 1 of the chamber and the mandrel 5, respectively. The piston has a through-flow channel 15 provided with a valve body 16 which is biased by a spring 17. These members allow the pressure medium to flow from the space 18 behind the piston to the space 19 upon a predetermined overpressure in the former in relation to the latter space.

The rear part 18 of the pressure chamber is not shown in detail. It may be provided in known manner with a lid and a pipe for introducing pressure medium into the chamber. The pressure in the chamber is increase to the value required for the extrusion by pumping the medium under high pressure into the chamber of by inserting a pressure-generating piston in the v chamber after it has been filled with pressure medium.

In the method according to the invention, the billet is preferably shaped as shown in FIG. 2. The core 7 is hollow with an inner diameter which gives free play with respect to the mandrel 5. The front end of the core is bevelled, for instance by turning. The casing 8 is tubular with an inner diameter which gives free play with respect to the core and is bevelled at its front end. Core and casing are then fixed together in the manner described above, and the necessary sealing means are applied at the rear end of the billet. The billet can now be upset. This can be done with the help of a tool 20 shown in FIG. 2. The tool has a conical depression with a top angle which is suitably in substantial agreement with the angle of a corresponding depression in the die 3. The recess has a peg 21 with a diameter substantially in agreement with the diameter of the mandrel 5.

The billet is fitted over the peg 21 and, by applying a force F to the rear end of the billet, this is pressed against the tool so that the front end of the core is upset inwardly towards the peg and the front part of the casing is upset inwardly towards the core. After upsetting, the billet has the shape shown in FIG. 1 and can be inserted in the pressure chamber in the position shown in FIG. 1, after which the pressure in the chamber is increased to the level required for extrusion.

Since the billet is shaped in this way, only the casing will be in contact with the die at the start of the extrusion process and only the core in contact with the mandrel. The contact line between core and casing will therefore face the atmosphere in the egress space. Thus all risks of pressure medium penetrating between core and casing are completely eliminated. This risks are a considerable drawback in previously known extrusion processes in which the contact line of core/casing faces the conical surface of the die, for example. The core and easing are preferably bevelled so that in the finished billet the ratio between the area of the material in core and casing is the same for each cross section perpendicular to the axis of the billet. The finished product will then have the desired ratio between core and casing area right from the start of the extrusion process and scrapping need not occur.

The upsetting may also be performed after the billet has been applied in the pressure chamber. The billet, in the form shown in FIG. 2, is then inserted in the pressure chamber and this is sealed. The pressure medium is introduced into the space 18 and the pressure increased. The piston 12 then presses the billet against the die so that upsetting takes place and the core 7 is brought into contact with the mandrel and the casing 8 with the core 7. The pressure from the piston 12 is determined by the valve 15, 16, 17 which is set so that sufficient force is obtained for upsetting before the pressure medium is allowed into the space 19. During the upsetting the billet will be brought to seal against the mandrel and the die and since only after this is the pressure medium introduced into the space 19, leakage is prevented through the die opening.

The process and billet described can be used for manufacturing tubing of widely differing combinations of material and this offers great advantages since each material canthen be individually selected having the best properties with respect to specific requirements such as electric or thermal conductivity, density, price, electrical contactability, corrosion resistance, hardness, etc.

The method and the billet may also be used for combinations of more than two materials, in which case several casings may be applied one on top of the other on the core.

Similarly, tubes of arbitary shape for the cross section within wide limits can be manufactured.

It is advisable to clean the surfaces of core and casing which face each other prior to the extrusion, removing excessive oxidation, grease and the like. However, it is not usually necessary to thoroughly clean the surfaces and normal layers of oxide forming during storage of the metal can usually be left without any deterioration of the bond between core and casing being caused in the finished product.

I claim:

1. Method of manufacturing tubes of compound material having an inner tube (7) and at least one outer tube surrounding the inner tube, which comprises forming a billet by mounting a hollow core (7) and a tubular casing (8) in coaxial relation to each other, and hydrostatically extruding the billet through an opening in a die (3) from a pressure chamber (1, 2, 3) containing a pressure medium to an egress space, a mandrel (5) being arranged in the opening of the die in such a way that a gap (6) corresponding to the thickness of the wall of the finished tube is'formed between the mandrel and the opening, in which, at the start of the extrusion, when the billet is brought into contact with the die (3) and the mandrel (5), only the casing (8) abuts the die (3) and only the core part (7) abuts the mandrel (5), whereby the parts of both the core (7) and the casing (8) located nearest the opening are in direct communication with the egress space by way of the gap (6).

2. Method according to claim 1, in which the opening has a section which expands conically towards the pressure chamber, the end of the casing facing the die being bevelled to an angle approximately corresponding to the angle of inclination of said conical part.

3. Method according to claim 1, in which the casing (8) and the core (7) are bevelled prior to extrusion, with their wall thickness decreasing towards the end of the billet facing the die.

4. Method according to claim 3, in which, in the bevelled portions of the casing (8) and the core (7), in each cross-section of the billet perpendicular to the direction ofthe extrusion the ratio between the area of material in the core and in. the casing is the same.

5. Method according to claim 1, which includes fitting the casing (8) over the core (7) and fixing it thereto in the axial direction, and thereafter bringing the end of the casing facing the die into abutment with the core by upsetting it.

6. Method according to claim 1, which comprises upsetting the end of the billet facing the die before the bi]- let is inserted in the pressure chamber.

7. Method according to claim 5, which comprises inserting the billet in the pressure chamber and pressing the billet against the die (3) to upset the end facing the die.

8. Method according to claim 7, which comprises bringing the core (7) into abutment with the mandrel during the upsetting.

9. Method according to claim 7, in which a piston (12), sealed against the pressure medium, is arranged in the pressure chamber dividing it into a part (19) where the billet is located and a second part (18), which comprises introducing the pressure medium into the second part under sufficient pressure to cause the piston to exert sufficient force on the billet to produce such upsetting.

10. Method according to claim 9, which comprises, after the upsetting, allowing the pressure medium to core.

12. Method according to claim 1 which comprises attaching the core and the casing to each other prior to the extrusion so that axial displacement of the core in relation to the casing is prevented in the pressure chamber during the extrusion process. 

1. Method of manufacturing tubes of compound material having an inner tube (7) and at least one outer tube surrounding the inner tube, which comprises forming a billet by mounting a hollow core (7) and a tubular casing (8) in coaxial relation to each other, and hydrostatically extruding the billet through an opening in a die (3) from a pressure chamber (1, 2, 3) containing a pressure medium to an egress space, a mandrel (5) being arranged in the openIng of the die in such a way that a gap (6) corresponding to the thickness of the wall of the finished tube is formed between the mandrel and the opening, in which, at the start of the extrusion, when the billet is brought into contact with the die (3) and the mandrel (5), only the casing (8) abuts the die (3) and only the core part (7) abuts the mandrel (5), whereby the parts of both the core (7) and the casing (8) located nearest the opening are in direct communication with the egress space by way of the gap (6).
 2. Method according to claim 1, in which the opening has a section which expands conically towards the pressure chamber, the end of the casing facing the die being bevelled to an angle approximately corresponding to the angle of inclination of said conical part.
 3. Method according to claim 1, in which the casing (8) and the core (7) are bevelled prior to extrusion, with their wall thickness decreasing towards the end of the billet facing the die.
 4. Method according to claim 3, in which, in the bevelled portions of the casing (8) and the core (7), in each cross-section of the billet perpendicular to the direction of the extrusion the ratio between the area of material in the core and in the casing is the same.
 5. Method according to claim 1, which includes fitting the casing (8) over the core (7) and fixing it thereto in the axial direction, and thereafter bringing the end of the casing facing the die into abutment with the core by upsetting it.
 6. Method according to claim 1, which comprises upsetting the end of the billet facing the die before the billet is inserted in the pressure chamber.
 7. Method according to claim 5, which comprises inserting the billet in the pressure chamber and pressing the billet against the die (3) to upset the end facing the die.
 8. Method according to claim 7, which comprises bringing the core (7) into abutment with the mandrel during the upsetting.
 9. Method according to claim 7, in which a piston (12), sealed against the pressure medium, is arranged in the pressure chamber dividing it into a part (19) where the billet is located and a second part (18), which comprises introducing the pressure medium into the second part under sufficient pressure to cause the piston to exert sufficient force on the billet to produce such upsetting.
 10. Method according to claim 9, which comprises, after the upsetting, allowing the pressure medium to enter into the part (19) of the chamber where the billet is located, and increasing the pressure to a level sufficient to produce extrusion.
 11. Method according to claim 1 which comprises applying to the end of the billet facing away from the die sealing means (9) which prevent the pressure medium from penetrating between the casing and the core.
 12. Method according to claim 1 which comprises attaching the core and the casing to each other prior to the extrusion so that axial displacement of the core in relation to the casing is prevented in the pressure chamber during the extrusion process. 